Cooling Fan
Cooling Fan Description and Operation
One Cooling Fan-3 Relays
System Overview
The engine cooling fan system consists of one electrical cooling fan, a serviceable resistor module mounted in the cooling fan shroud, and three fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate the fan at low, medium, or high speeds, depending on cooling requirements. The cooling fan and fan relays receive battery voltage from the underhood fuse block. The ground path for the operation of the cooling fan is provided at G104.
Low Speed Operation
The ECM energizes the fan 1 relay by grounding the fan 1 relay control circuit. The fan 1 relay coil closes the relay contacts to supply battery voltage from the FAN 1 fuse through the high resistance circuit of the cooling fan resistor module, and the fan motor supply voltage circuit to operate the cooling fan at low speed.
Medium Speed Operation
The ECM energizes the fan 2 and S/P relays by grounding the fan 2 relay control circuit. The energized fan 2 relay coil closes the relay contacts to supply battery voltage from the FAN 2 fuse. The voltage passes through the medium resistance circuit of the cooling fan resistor module, and the fan motor voltage supply circuit to operate the cooling fan at medium speed. At the same time, the energized S/P relay coil switches the dual pole contact position to prevent voltage from passing through the S/P relay to the low resistance circuit of the resistor module.
High Speed Operation
The ECM energizes the fan 1 relay by grounding the fan 1 relay control circuit. The ECM also energizes the high speed fan 2 relay and the S/P fan relay by grounding the fan 2 relay control circuit. The energized S/P fan relay coil switches the dual pole contact position, allowing voltage from the FAN 1 fuse to pass through the S/P relay to the low resistance circuit of the cooling fan resistor module, and the motor voltage supply circuit to operate the cooling fan at high speed. The energized fan 2 relay also provides voltage from the FAN 2 fuse through the medium resistance circuit of the cooling fan resistor module. This provides a back up to high speed operation if a condition exists in the high speed cooling fan circuit.
Two Cooling Fans-3 Relays
System Overview
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds, depending on cooling requirements. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G104 and G101.
Low Speed Operation
The ECM supplies the ground path for the low speed fan 1 relay through the fan 1 relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the FAN 1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the cooling fan S/P relay and the left cooling fan. The result is a series circuit with both fans running at low speed.
High Speed Operation
The ECM supplies the ground path for the fan 1 relay through the fan 1 relay control circuit. After a 3 second delay, the ECM supplies a ground path for the high speed fan 2 relay and the fan S/P relay through the fan 2 relay control circuit. This energizes the fan S/P relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time, the fan 2 relay coil is energized closing the relay contacts, and provides battery positive voltage from the FAN 2 fuse on the cooling fan motor supply voltage circuit, to the left cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.